Semiconductor chips which are used in chip cards, for example credit or payment cards, telephone cards and the like, are susceptible to attacks for decoding the memory contents or the functions of the chip. Such attacks commonly occur by an FIB technique, in which a focused ion beam is directed onto the chip. The impact of the ions from the ion beam ablates the layers of the semiconductor chip, thereby allowing the layer-wise structure of the chip to be studied. A surface-wide metal coating to the chip offers passive protection against FIB this.
Polymers having extended π-systems are the basis for organic semiconductors. Such dielectrics can therefore be regarded as organic semiconductors having an extremely low charge-carrier mobility. The ohmic conductivity of dielectrics based on polymers having extended π-systems increases by orders of magnitude when they are doped.
Polyaromatics, as described for example in International Publication Nos. WO 97/10193 and WO 98/11149, polyimides, polybenzoxazoles, polyimidazoles or polyethers are primarily used as dielectrics having extended π-systems. The polymer backbone may contain further heteroatoms, for example sulphur.
Irradiation of the dielectric by means of ions, as occurs during an FIB analysis, leads to a local increase in the ohmic conductivity by orders of magnitude. The dielectric becomes irreversibly doped by this.
German Patent No. DE 100 44 837 C1 describes a circuit arrangement for detecting an undesired attack, and especially one using FIB, on an integrated circuit, in which a clock signal is applied to a signal line. The signal line and a line pair, which is used for encoding a bit, are interconnected between two circuit blocks of the integrated circuit, and are connected to a detector circuit which changes the functionality of the integrated circuit as a function of the signals on the signal line and the line pair.
European Patent Publication No. EP 1 109 220 A2 and IBM Technical Disclosure Bulletin 34, 366 (1992) disclose polybenzoxazole and polyimide as a dielectric material for, respectively, electrical installation and passivation on semiconductor components.
It is an object of the present invention to provide a semiconductor chip having FIB protection, which can be used universally.